167. Two Sum II - Input Array Is Sorted

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Problem

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.

Note:

Your returned answers (both index1 and index2) are not zero-based. You may assume that each input would have exactly one solution and you may not use the same element twice. Example:

Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.

Code

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        if(numbers == null || numbers.length < 2) return new int[]{-1, -1};

        int left = 0;
        int right = numbers.length - 1;

        while(left < right){
            int sum = numbers[left] + numbers[right];
            if(sum == target){
                return new int[]{left + 1, right + 1};
            } else if(sum > target){
                right--;
            } else {
                left++;
            }
        }

        return new int[]{-1, -1};
    }
}